As exemplified by U.S. Pat. Nos. 4,779,673 and 5,022,459 to Chiles et al., flexible hoses having a multiple layer construction have been used effectively in heat exchange applications such as heating of floors, ceilings, roofs and concrete or asphalt slabs. The hose is normally embedded in a surface which is to be heated by hot water pumped through the hose. The flexibility of a hose makes it much better in this type of application than rigid plastic or metal pipes because a hose can be bent or curved more sharply and more easily than a rigid pipe. Often, the conduit must be turned sharply to accommodate floor or roof framing, and a hose can be used in many applications where it is virtually impossible to use a rigid pipe because of its inability to accommodate sharp turns.
Hoses are also effective in other applications that involve the flow of heat exchange fluids. For example, hoses that accommodate cooling fluids in vehicles and hoses that convey refrigerants are widely used.
One of the principal problems with the hoses that have been used in the past is that they have been subject to gas infiltration and exfiltration that can cause problems. For example, oxygen passing through the hose wall from the outside to the inside can accelerate the aging of the hose and significantly shorten its useful life. Oxygen infiltration can also cause undue oxygenation of the fluid flowing in the hose and can cause corrosion of ferrous plumbing components. The hose layers are usually constructed of elastomeric or thermoplastic compounds, and the organic gases that may be present in these materials can migrate through the hose wall and cause unpleasant odors in the space that is being heated by the radiant hose heating system.
There are several plastic compounds that are known to be effective gas barriers. In order to allow the hose to retain the necessary flexibility, a plastic gas barrier must be thin enough to avoid adding undue rigidity to the hose. As a consequence, the gas barrier must be provided as a thin layer, and it must be incorporated inside hose wall so that it is protected by the abrasion resistant cover.
However, significant problems are encountered in incorporating a thin plastic film as a gas barrier inside of a hose wall. Normally, the hose has a tube, a mesh fiber reinforcing grid around the tube, and a protective outer cover around the reinforcement. If the plastic film is applied around the tube and then covered with the fiber mesh, the fibers can shrink and cut through the barrier film during processing. As can easily be appreciated, this reduces or destroys the ability of the barrier to inhibit gas infiltration and exfiltration.
Problems are also encountered if the gas barrier is applied around the reinforcing grid. The barrier layer can flow into the grid openings, and this decreases its thickness and its effectiveness as a barrier to gases. If the barrier lays wholly on the reinforcement, air is trapped in the pockets that are presented by the grid openings. This air can become saturated with liquid, and steam can be created and can burst through the outer layer of the hose during processing. Even if a problem this severe does not develop, the trapped air reduces the heat transfer rate through the hose and thus detracts from the efficiency of the heating system.
Another problem is that materials that are effective as gas barriers are typically ill suited for adherence to the layers that are inside and outside of them. For example, the gas barrier has difficulty adhering to reinforcing fibers of the type that are commonly used, including nylon, rayon, polyester and aramid products. If adhesion is poor, the layers of the hose can delaminate while in service and cause the hose to fail prematurely.